Jose Miranda from Isabela, Puerto Rico was snapping pictures of one of the most famous nebulae in the sky. While looking at the images, he noticed a moving object. Miranda, who is affiliated with the Astronomical Society of the Caribbean, said:

It was clear the object was not a satellite because my images were of long exposure. Low to medium altitude orbiting satellites appear as long streaks or lines as they cross the whole field of view captured in the pictures.

The only satellites that can appear to move very slowly in a lapse of time are geosynchronous satellites as they orbit at about 23,000 miles above Earth’s surface. They seem static from a fixed point on our planet, but if you are observing a specific area of the sky though a telescope, then the satellite will be seen – very slowly – drifting in space as it orbits our planet.

In addition to six or seven moving satellites seen as brief lines on the images, the object that caught his attention appeared slowly moving through a lapse of time, which suggested it was an asteroid (or a geosynchronous satellite). Distant moving comets look similar, but usually appear as fuzzy objects.

Miranda consulted the images with his friend Jonathan Ospina, who utilizing software like Cartes du Ciel, which plots the current position of asteroids and comets, was able to identify the object as Asteroid 4451 Grieve.

4451 Grieve is a space rock in the asteroid belt. It occasionally crosses the orbit of planet Mars. It was discovered in 1988 by Carolyn Shoemaker at Palomar Observatory.

Its appearance in front of the nebula is a matter of perspective since the asteroid is relatively close in our solar system, while the Horsehead Nebula is located at 1,500 light-years, or 9,000 trillions of miles in the direction of the Orion constellation.